1. Field of the Invention
The present invention relates to drilling in the oil field industry and more particularly to a downhole circulating tool with a cam slot having continuous and symmetrical wishbone patterns through which a cam pin moves to alternate fluid port openings.
2. General Background
Drilling fluid is pumped down through a circulating tool to a drill bit. The fluid returns to the surface through the annulus defined between the string and the borehole wall or bore-lining casing. However, the drill cuttings may settle in the bore if the flow rate of the returning fluid is not sufficiently high. The circulating tool circulates the fluid in the borehole annulus to facilitate removal of drill cuttings which have settled in the borehole. Moreover, the circulating tool improves removal of caked drilling fluid, cement and debris from the drilled casing plugs, most of which may be attached to the casing wall of a borehole.
Known circulating tools have sliding tubes (sometimes in multiples) with seals (e.g. soft seals). Seals are a concern of any circulating tool. The circulating tools may operate under high pressures (up to 3000 PSI) and high flow rates (e.g. 10-20 barrels per minute or more). Thus, a seal failure can be a disaster. A seal failure can not only disable the function of the tool but also damage the tool with washouts.
Some tools use a cam with an unequal pin travel. Others have many seals needed for the tool to work which require manufacturing precision and a restriction to make the tool shift.
Thus, there is a need for techniques to improve the circulation of the drilling fluid to facilitate the removal of settled drill cuttings and/or borehole debris.